Philips - REM XL 40

The XL 40 manufactured by Philips is a scanning electron microscope with an extra large sample chamber. Data is captured using SE-, BSE- und EDX-detectors. 

Functional Principle

Inside a scanning electron microscope, an electron beam is driven over the sample along a grid. The beam is generated using a heated tungsten filament as emitter. A magnetic field produced by inductors is able to divert the electron beam, similarly to old tube televisions. A number of interactions occur if the beam hits the sample. These are captured by various detectors, enabling a characterization of the sample.

To avoid interaction with the particles present in the air, the whole process is conducted in a vacuum.

Secondary Electron Detector (SE-Detector)

Secondary electrons are created if the electrons of the electron beam and the weakly bound conduction band electrons of the sample’s atoms interact. Only the secondary electrons created near the sample surface can leave the sample. Therefore the detected secondary electrons are mostly used to generate a topographical image of the probe.

Backscatter Electron Detector (BSE-Detector)

By having elastic collisions with the sample atoms, part of the beam electrons are scattered back from the sample, depending strongly on the sample’s mean atomic number. The electrons are scattered more if colliding with heavier elements, resulting in a brighter image-pixel at the corresponding location.

Energy Dispersive X-Ray Analysis (EDX-Detector)

If a beam-electron knocks out an electron close to the core of a sample’s atom, this electron is replaced by an electron from a higher energetic electron shell. The difference in energy between the shells is emitted as roentgen radiation (X-rays). Since energy and wavelength of the radiation are characteristically for the element, its analysis gives information about quantity and distribution of present elements within the sample.